Added rethink unique_db fixture
Added rethink_module_db(), rethink_make_tables() and rethink_empty_db() to make it possible to construct the database and required tables once, emptying them between tests, rather than rebuilding db and tables for each test.
Merge pull request #45 from agiledata/reorganise_testing

Added rethink_module_db(), rethink_make_tables() and rethink_empty_db() ...
Merge pull request #46 from ahlmss/reorganise_testing

Reorganise testing